Biodiesel (mono alkyl esters) is a cleaner-burning diesel fuel made from natural, renewable sources such as vegetable oils. The practice of blending biodiesel into diesel fuel has been studied and practiced commercially for several years. Such blending operations have been widespread in “warm” periods defined as those occasions where the diesel fuel is not lower in temperature than the biodiesel Cloud Point or Pour Point. However there is limited experience with blending of biodiesel with diesel fuel that is below the biodiesel Cloud Point or Pour Point.
Diesel fuels are characterized, in part, by their relatively large carbon number. One result of the large carbon number is that the fuels are sensitive to low temperatures where some of the component compounds can begin to crystallize. The presence of solid crystals in the fuel affects the viscosity, volatility and the passage of the fuel through fuel filters. There are various measures applied to describe the crystallization tendency of a diesel fuel. The most common are pour point (ASTM D-97), Cloud Point (ASTM D-2500, ASTM D 5771, ASTM D 5773) cold filter plugging point ([P-309), and the low-temperature flow test (ASTM D-4539). All of these tests have the common goal of describing fuel plugging and/or crystallization at low temperatures.
Reported cases of blending biodiesel with diesel fuel in cold climates have involved adding “very hot biodiesel” to diesel fuel in splash blends. Some examples of this type operation were reported at the National Biodiesel Conference in February, 2004. For example, presenters from the Defense Energy Support Center stated that the optimum blending technique was that diesel fuel is picked up at a supplier loading rack and driven to a B100 supplier. The warm/hot B100 is added to the diesel fuel and blending occurs during transportation to the customer. The presenters also stated, however, that quality concerns arise because “improper blending during colder months can result in cloudiness, gelling, particulate formation or filter clogging.” Their only solution was that, due to colder climates, some areas of the country do not supply biodiesel in the winter, although heated tanks or tanks inside heated buildings are being added.
These examples represented “trial” programs and involved relatively small volumes of diesel fuel. In every reported example, B100 was diluted into diesel fuel. The present inventors are not aware of any current practice of in line blending of biodiesel into diesel fuel at a bulk fuel terminal in the north in the winter when diesel fuel can be below the biodiesel Cloud Point.
Addition of soy or other fatty acid based biodiesels as B100 to diesel fuel that is below 20° F. typically yields a separate phase that persists for “minutes” even when the cold diesel is subjected to significant mixing. This suggests that delivery of bright and clear product will be problematic at winter conditions where diesel fuel is below, to substantially below 20° F., which occurs regularly at cold weather terminals in Europe and in the United States, such as terminals at Pine Bend, Minn. and other terminals supplying the Minnesota market. The inventors are not aware of any known designs proven for in line blending of biodiesel fuels for delivery in “Minnesota cold” temperatures. This is of particular importance since the Minnesota 2% Biodiesel mandate became law on Mar. 15, 2002. This law is expected to require that all of the diesel fuel sold in the state contain at least 2 percent biodiesel after Jun. 30, 2005.